Archive for the ‘Do It Yourself’ Category:

2019-11-29 Electrostatic Field Sensing, BJT Versus MOSFET

The Facebook group Electrostatic and Electromagnetic Field Detectors (I’m a member) has shown the very low current sensor made of three BC547 BJTs (bipolar junction transistors). The three BJTs are connected as Darlingtons (I called them Trarlingtons) so they multiply the base current by their betas or current gains. For three transistors, assuming each has

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2019-11-26 My Radio As A Kid

from FB Comment Nov 26 I inherited old tube radios, I never had a boy’s radio, still don’t today. But I got a 2 transistor SupereX kit that I built. It was a crystal set with an earphone amplifier. Didn’t work very good because I lived a few miles from an AM transmitter and until

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2019-11-15 Build A LED Tester

Big Clive’s YouTube video Ohhh nooo! After all the trouble Big Clive went to show us how a Joule Thief works, he *digressed* to using a 9V battery for his LED tester! Horrors! 😱😱😱 I built a Joule Thief with a socket like he used for the LED. But the JT must not be left

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2019-11-07 Audio Impedance Matching Box

I’ve often had to kloodge together an audio transformer, jacks and other stuff to make a medium impedance output match a low impedance headphone. But it turns into a mess of wires and parts dangling from a transformer. I thought about what I would do to make a box with the necessary stuff, like inputs,

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2019-10-05 Huge Corcom Filters For RFI

from FB group post to Building Transistor Radios 2019 Oct 5 I spent quite a bit of time adding filtering to my 0 to 30VDC, 10A SMPS to get rid of the RF interference. It was successful, I got rid of most of it, but not all. So I think I found the solution. This

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2019-09-09 Zenith Royal 475 Information

more text below Zenith Royal 475 ARF project & service info links: https://antiqueradios.com/forums/viewtopic.php?f=4&t=233319 https://www.antiqueradios.com/forums/viewtopic.php?f=4&t=226370 https://www.antiqueradios.com/forums/viewtopic.php?f=4&t=235052 The Zenith factory schematic and PCB layout is located on page 185 of the Beitmans service literature which is freely available on-line: https://www.americanradiohistory.com/Archive-Rider/BEITMAN-SUPREME/Beitman-1961.pdf ** also posted to FB group vintage transistor radios Usually the capacitors are the problem. There are

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2019-07-06 Earliest Audio Amplifiers I built

from FB group Building Transistor Radios July 6 Bill Korbak The early germanium alloy transistors didn’t have enough bandwidth for RF, they were only good for audio. That’s where I built my first amplifier, a three transistor audio amp on a PC board I etched in ferric chloride. I also built the power amplifier. It

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2019-06-12 Plug-in Coils Pros And Cons

from FB group Regenerative Radio… Jun 13 I’ve thought about using plug-in coils, but I’ve had experience with Grid dip meters and there are a few important issues that must be dealt with. One is, what happens to the unused coils when the equipment is not in use. They get separated from the equipment and

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2019-06-11 Selenium Rectifier Burned Up, How To Replace

from FB group Vintage Transistor Radios Jun 12 Bob Kirsch has the right idea, but the single replacement diode *must* be rated for 400 V peak inverse voltage or more. A 1N4007 is cheap and readily available. I assume you’re in a country where the AC line voltage is 120 VAC, because the rectified DC

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2019-05-31 DIY Plastic Variable Capacitor

I hear others complain about the high cost of variable capacitors, especially the older air variables with metal plates. So I decided to DIY and make one. This is my first attempt so forgive the lack of elegance and unfinished look. I’m sure it could be improved on and made better with some effort. The

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